A KINETIC THEORY OF MATTER. 227 



temperature hypothesis proves some degree of 

 attraction among the molecules, but it does not 

 prove ultimate attraction between two molecules 

 in collision, or at distances much less than the 

 average mutual distance of nearest neighbours in 

 the multitude. The collisional force might be 

 repulsive, as generally supposed hitherto, and yet 

 attraction might predominate in the whole 

 reckoning of difference between the intrinsic 

 potential energies of the more dense and less 

 dense multitudes. It is, however, remarkable 

 that the explanation of the propagation of sound 

 through gases, and even of the positive fluid 

 pressure of a gas against the sides of the con- 

 taining vessel, according to the kinetic theory 

 of gases, is quite independent of the question 

 whether the ultimate collisional force is attractive 

 or repulsive. Of course it must be understood 

 that if it is attractive, the particles must be so 

 small that they hardly ever meet they would 

 have to be infinitely small to never meet that, 

 in fact, they meet so seldom, in comparison with 

 the number of times their courses are turned 



Q 2 



